Daniel Gladow, Sebastian Doniz‐Kettenmann, H. Reissig
Jun 1, 2014
Citations
0
Influential Citations
20
Citations
Journal
Helvetica Chimica Acta
Abstract
The 1,3-dipolar cycloadditions of ethyl 2-diazo-3,3,3-trifluoropropanoate with electron-rich and electron-deficient alkynes, as well as the van AlphenHuttel rearrangements of the resulting 3H-pyrazoles were investigated. These reactions led to a series of CF3-substituted pyrazoles in good overall yields. Phenyl- and diphenylacetylene proved to be unreactive, but, at high temperature, the diazoalkane and phenylacetylene furnished a cyclopropene derivative. As expected, the 1,3-dipolar cycloaddition to the ynamine occurred much faster than those to electron-deficient alkynes. With one exception, all cycloadditions proceeded with excellent regioselectivities. The [1,5] sigmatropic rearrangement of the primary 3H-pyrazoles provided products with shifted acyl groups; products resulting from the migration of a CF3 group were not detected. In agreement with literature reports, this rearrangement occurs faster with 3H-pyrazoles bearing electron-withdrawing substituents.